A vehicle seat for multipurpose use, for a example disclosed in U.S. patent application Ser. No. 5,498,051, usually is provided with a first lock unit provided with a rotational axis and supported on the vehicle floor at the front end portion of the seat device. Also, the seat has a second lock unit at the rear end portion of the seat device. The first and second lock unit are arranged to be able to engage with or release from a first and a second strikers fixed on the vehicle floor.
The second lock unit is released from the second striker, then the seat can be rotated around the rotational axis of the first lock unit and made to stand up as its front portion to be lower, that is, as the seat to be in tumbled condition. Further, by operating a hook installed on the first lock unit to release the engagement from the first striker, the seat can be removed from the floor. Thus, the cargo space on the floor can be expanded.
Usually, in the seat, as above mentioned, which can be arranged to be in tumbled condition, the hook of the first lock unit is possible to be released even when the seat is not in tumbled condition. For example, even when the seat is in sitting use condition of the occupant, the first lock unit may be released. It is difficult to restore the seat to be in sitting use condition again, because the seat may take several postures.
Also, the distance between the first and second lock units and the first and second strikers varies depending on manufacturing or assembling tolerance. This generates difficulty of locking operation or over load on the lock units when the seat is restored to be in the sitting use condition from the tumbled condition.